Floating solar power plant with asymmetrical concentrators

FIELD OF THE INVENTION

The invention comprises a circular solar platform floating on a shallow layer of water, rotatable about its vertical axis with concentrator channels arranged parallel to each other. The lower surfaces of the channels carry photovoltaic cells extending into the water layer. The concentrator channels are designed in such a way that they enclose air passages which, during hours without sunshine, are positioned in such a way that they run parallel to the direction of the wind.

PRIOR ART

German patent application DE 44 04 295 describes a floating solar power plant in which the concentration of the solar rays is performed by the prisms of a linear lens in which the solar rays undergo an internal reflection. The disadvantage of this design is that the waste heat from the photovoltaic cells, stored in the water layer 9, cannot be sufficiently dissipated to the ambient air.

SUMMARY OF THE INVENTION

The principal idea of the invention consists of air passages through which wind currents can pass. This is achieved by concentrator channels with one almost vertical wall. The lower end of this wall lies below the water level and is in intimate heat conducting contact with the photovoltaic cells. Such a design requires a roof-forming lens with one section comprising the prisms of a Fresnel lens and another section in which the considerable bending of the rays, which cannot be accomplished with Fresnel lenses, is achieved by prisms in which a total reflection of the solar rays takes place.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the principle of optical tracking.

FIG. 2 shows a portion of a solar power plant as described in the invention.

FIG. 3 shows the path of rays within the linear lens.

FIG. 4a shows a cross-section through a concentrator channel.

FIG. 4b shows the end-section of a concentrator channel.

FIG. 5a shows the pencil of rays in one extreme situation.

FIG. 5b shows the pencil of rays in the opposite extreme situation.

FIG. 6 shows a row of secondary concentrators.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the symbolized path of the solar rays being refracted downwards by the upper layer 1, and being concentrated onto the photovoltaic cell 3 by the prism 2 of the second layer.

FIG. 2 shows a portion of a floating solar platform in which the elongated concentrator channels 4 are shown in cross section. The water layer 8 is separated from the subsoil by a plastic membrane 5 which is surrounded by a circular wall 6. A central bearing 7 centrally locates the platform floating on the water layer 8. During sunshine hours the platform follows the sun's azimuth; during overcast and night hours a wind sensor causes the platform to turn such that the concentrators run parallel to the direction of the wind.

FIG. 3 shows an enlarged cross-section of the linear lens. The upper layer 1 has a smooth upper surface 21. On its downward-facing side it has steps 18 which are divided into two optical boundary layers 19 and 20. The lower layer 22 has steps 23 on its upward facing boundary face with the same spacing as the steps 18. The edges of steps 23 are in contact with the separating line between the two optical boundary layers 19 and 20. Flanks 38, not penetrated by solar rays, run almost vertical. The downward-facing side of the lower layer 22 has sharply-angled prisms 24 running perpendicular to the steps 18 and 23. These prisms 24 concentrate the solar rays onto focal lines running parallel to prisms 24. Solar rays 25 undergo a total reflection on the right flanks 17 of prisms 24 in the sharply-angled section 11 shown in FIG. 5. From there they exit as rays 26 onto a focal line.

FIG. 4a shows a vertical cross section through concentrator channel 4. The trough 41, 43, 42 whose wall 41 runs vertical, floats on water layer 48, whereby the bottom region 43 is slightly submerged in the water layer. The roof of the concentrator channel 4 is formed by parabolically-bent linear lenses 40. These lenses are divided into two sections; one section 11 has sharply-angled prisms which strongly bend the rays, and a second section 12, resembling a Fresnel lens which slightly bends the rays. The remaining triangular channel 44 acts as a wind passage through which the ambient air can flow, thus cooling the water layer 48 in which the waste heat of the photovoltaic cells has been stored. In areas in which the air is relatively free of dust the diagonal wall 46 can be eliminated. Wall 41 has a groove 47 which acts as a rail on which a maintenance cart can be run. Wall 41 and wall 42 form a channel 51 through which rain water can flow down into water layer 48.

FIG. 4b shows the end section of a concentrator channel. The lower wall portion 55 is sealed to the bottom area 43 and the vertically extending wall sections from walls 41 and 42. Above this area a triangular wall 56 is inserted which prevents dust from entering the concentrator channels.

FIG. 5a shows the pencil of rays 31 formed by the strongly-bending section 11 when the sun's elevation is centrally located between the highest and the lowest elevation. The focal line 33 of the pencil of rays 31 then lies above focal line 32 of the pencil of rays 34 which is formed by the Fresnel prisms in section 12.

FIG. 5b shows that the focal lines 32 and 33 for the lowest useable elevation and the maximum elevation have changed places compared to the situation described in FIG. 5a.

FIG. 6 shows a secondary concentrator system to increase the concentration on the photovoltaic cells 60. These secondary concentrators 62 and 63 concentrate three-dimensionally, in the plane of the drawing as well as in the plane perpendicular to it. This minimizes the necessary surface of photovoltaic cells (60) as well as the cost of the cells. This reduction is possible because the waste heat of the photovoltaic cells (60) is dissipated through the metal wall of the troughs into the water layer (48). The secondary concentrators (62 and 63) are in contact with each other along line (64) so that the total concentrated radiation will reach the photovoltaic cells (60).